Composites with a thermosetting resin as the matrix are widely used in various areas such as aerospace area, sporting area, civil engineering and architecture area since they are light in weight and excellent in mechanical properties, corrosion resistance, etc. So far, various prepregs as combinations of a thermosetting resin and reinforcing fibers, and composites made from them are known. Above all, prepregs made from an epoxy resin and carbon fibers are excellent in specific strength and specific elastic modulus, and the composites fabricated from them are excellent in such properties as heat resistance and compressive strength.
A prepreg is obtained by impregnating reinforcing fibers such as carbon fibers with a matrix resin such as an epoxy resin, and can be produced by any of various methods. A prepreg is typically produced by preparing a resin coated film with a matrix resin laminated on a releasable film such as paper and a reinforcing fiber sheet with reinforcing fibers such as carbon fibers arranged like a sheet, and overlaying the resin coated film on one or both sides of the reinforcing fiber sheet, with the resin side kept inside, and heating and pressing them, to impregnate the reinforcing fibers with the resin.
In general, a composite with a thermosetting resin as the matrix resin is brittle and weak in impact.
Depending on applications, a prepreg with higher impact resistance is necessary. For example, Japanese Patent Laid-Open (Kokai) No. 1-104624 discloses an interlaminar particle reinforced prepreg with thermoplastic resin particles as a surface layer, to ensure that when a plurality of layers of the prepreg are laminated, particles made of a highly tough thermoplastic resin are localized between laminate layers.
However, the prepreg produced according to this technique is limited in applicability to an area requiring a compression interlaminar shear strength, since it declines in compression interlaminar shear strength (CILS), though highly improved in impact resistance. Furthermore, an interlaminar particle reinforced prepreg has a disadvantage that the tackiness described later is generally low, compared to a prepreg without containing particles.